For input to mobile devices, a screen that can be provided in constituting input devices is restricted, and thus it is difficult to realize a keyboard on which many keys are arranged so as to generate various input signals or to display a great number of icons on the same screen. To display a large number of keys or icons on a screen, the size of each key or icon is required to be reduced, and in this case, visibility is reduced and there is an increasing possibility of malfunction in a process of selecting a small-sized key or icon.
In the case of character input, for example, mobile devices have a limitation such as the use of only one finger or two fingers due to characteristics thereof. To input a large number of characters using a small number of keys, it is required to use a method of assigning several characters to a single key and then identifying the assigned characters.
One example is a method of assigning several characters to a single key and then identifying the assigned multiple characters depending on how many times the corresponding key is touched. That is, there is a method of identifying multiple characters by selecting the first character by touching the corresponding key only once, selecting the second character by consecutively touching the corresponding key twice, and selecting the nth character by touching the corresponding key n times.
As another example, there is a method of assigning a plurality of characters to one key, and then rendering keys having the assigned characters activated around the input key when the corresponding key is touched, and selecting any one of the activated keys, or a method of searching for a desired character by repeatedly applying this method and inputting the character.